1. Field of the Invention
The present invention relates in general to cooling systems suitable to be used with engines of heavy equipment and of construction vehicles and, more particularly, to a structural improvement in such cooling systems for controlling volumes of air delivered by a cooling fan in order to achieve the optimal cooling effect regardless of engine revolutions.
2. Description of the Prior Art
The temperature of combustion gas in a cylinder of an internal combustion engine typically ranges from 2,000.degree. C. to 2,300.degree. C. Most of the heat from the hot combustion gas is absorbed by engine parts such as the cylinder, the cylinder head and the pistons. When the above engine parts become overheated as a result of absorption of the combustion gas heat, either the cylinder may be deformed or the oil film on the cylinder wall may be broken, thus causing improper lubrication of the engine. What is worse, such improper lubrication may cause engine trouble. When the engine parts become overheated as described above, the combustion conditions of the engine become worse and this may generate knocking or pre-ignition of the engine and abruptly reduce the engine output power.
On the contrary, subcooling of the engine will cause a considerable amount of combustion heat to be lost, so that such subcooling of the engine will reduce the thermal efficiency of the engine increasing fuel consumption.
With reference to FIG. 1, there is shown In a block diagram a cooling water circulation circuit of a typical engine cooling system used in heavy equipment.
As shown in this drawing, the typical engine cooling system is a forced circulation cooling system using a water pump designated by the numeral 1. That is, cooling water contained in a water tank 2 is forcibly pumped up by the water pump 1 and passes through heated engine parts such as the cylinder block 3 and the cylinder head 4 of the engine 5. Of course, it should be understood that another coolant instead of the cooling water may be used for cooling the engine 5. While passing through the heated engine parts, the cooling water absorbs the heat of the engine 5 so that the temperature of the cooling water rises. The hot cooling water in turn is introduced into a radiator 8 connected to the cylinder head 4 through a hot water conduit 13. While passing through the radiator 8, the hot water is cooled to a temperature appropriate for optimal operating. The cooled water is, thereafter, returned to the water tank 2 through a cooling water return conduit 10. The above cooling water circulation is repeated during the engine operation.
Placed in back of the radiator 8 is a cooling fan 9 which is coupled to a crankshaft 12 through a fan belt 11. The crankshaft 12, which is rotated by the engine 5, thus rotates the cooling fan 9. The cooling fan 9 produces air currents in order to deliver large volumes of air to the radiator 8, which air passes through the gaps between cooling fins (not shown) of the radiator 8. While passing through the gaps between the cooling fins, the air absorbs the heat of the radiator 8, so that the cooling effect of the cooling system is promoted and the overheated engine 5 is more rapidly cooled.
A water temperature controller 6 is coupled to the hot water conduit 13 between the cylinder head 4 and the radiator 8. This controller 6 directly drains the cooling water to the water tank 2 through a bypass 7 when the water temperature is lower than a predetermined temperature (about 60.degree. C). However, the controller 6 is to introduce the hot cooling water into the radiator 8 when the water temperature is higher than the predetermined temperature. The cooling water, after being sufficiently cooled in the radiator 8, is returned to the water tank 2 through the cooling water return conduit 10.
When the heavy equipment, having the above engine cooling system, carries out work while running on a site, the cooling fan of the above engine cooling system is rotated by the crankshaft at an appropriate speed and produces currents in order to deliver sufficient volumes of air to the radiator, thus promoting a cooling effect of the radiator and to effectively cool the heated engine. However, when the heavy equipment carries out work while being stopped on a site, the crank shaft rotates at low speed, thus rotating the cooling fan at low speed. In this case, the cooling effect of the cooling system is remarkably reduced.
As well known to those skilled in the art, heavy equipment as well as construction vehicles should often carry out heavy work for long periods while being stopped on a site, which heavy work usually requires high output power of the engine. The engine of the heavy equipment or of the construction vehicle thus may be often overheated. The engines of the heavy equipment and of the construction vehicles, therefore, need to be provided with effective cooling systems.